This invention relates to a rotating electrical machine of the type that employs permanent magnets and cooperating coil windings wound around armature cores in confronting relationship to the permanent magnets.
A wide variety of types of electrical machines have been provided of the type mentioned in the preceding paragraph. These arrangements may be used as either motors or generators and either the magnets or the coil or both may rotate. If the device is an electrical motor, the windings are selectively energized so as to effect rotation. If the device operates as a generator, the relatively rotatable member is rotated and an electrical current is induced in the windings.
In conventional constructions of this type, the permanent magnets are disposed at circumferentially spaced even intervals with their polarity oppositely arranged. The electrical windings are formed on armature poles formed by a member that defines slots between it. The armature poles are also mounted at circumferentially spaced regular intervals.
With this type of mechanism, it is desirable to insure that the torque required to rotate the rotatable member without large power input is important. The torque necessary to achieve this rotation is referred to as “cogging torque”. If the cogging torque is large and the device is a generator, it requires large power to drive the mechanism and this increases the vibration. If the device operates as a motor and has high cogging torque, large power is consumed when idling and this also increases the vibration.
Basically, the cogging torque is related to the number of peak pulses in the coil windings per revolution of the rotor, referred to as the “cogging number”. The cogging number is generally equal to the least common multiplier of the number of slots and the number of magnetic poles. The cogging torque is basically proportional to the reciprocal of the square of the cogging number.
In addition, the multiple armature cores generally have the coils wound in coil groups or phases. In a conventional type mechanism, the coils of each phase are disposed adjacent to each other and are oppositely wound. This has the disadvantage of causing unbalanced magnetic forces, which can cause vibration and, in addition to the objectionable noise, premature wear of the bearings of the machine.
These disadvantages of the prior art structure may be best understood by reference to FIGS. 1 through 4, which show a prior art type of eight (8) pole nine (9) slot machine. FIG. 1 illustrates the winding of a prior art electrical motor or generator. FIG. 2 shows the cogging torque in relationship to the rotational angle. FIG. 3 which shows the counter EMF both between lines and phases. FIG. 4 which is a diagrammatic view showing the flux lines during a portion of the rotation of this machine.
In the illustrated embodiment, the machine includes a rotor, indicated generally by the reference numeral 21 which is comprised of a disk having a plurality of permanent magnets 22 fixed thereto around its periphery and which is affixed to a rotor shaft 23. The magnets 22 are formed from a ferromagnetic material, which is assembled to the disk and mounted on the shaft 23, and the magnetic material permanently magnetized. The assembly is bonded together with a resin.
A cooperating armature 24 has a plurality of armature cores that are separated by gaps or slots 25. These gaps or slots 25 are equally spaced around the circumference and around the axis of rotation of the rotor shaft 23.
Although the structure is described in conjunction with an arrangement with rotating magnets and fixed coil windings, the arrangement can obviously be reversed wherein the magnets are held against rotation and the coil windings rotate.
The armature cores that define the slots 25 are divided into groups, in this embodiment, these comprise three groups, having individual adjacent windings UUU, VVV, and WWW, respectively. Individual windings 26U, 26V and 26W are wound around the adjacent cores in opposite directions. As a result, the magnetic flux is such that it is unbalanced because of the fact that the adjacent windings of the coil phases are wound in opposite directions as to increase the magnetic flux as shown in FIG. 4.
The example shown employs nine slots and eight magnetic poles and thus, has a cogging number of 72 i.e. 9×8. Thus, although this type of mechanism provides a low cogging torque as seen in FIG. 2 and a fairly uniform counter electromotive force as shown in FIG. 3, it results in vibrations and the total power output is not as great due to the fact that the coils operate in sequence and thus, tend to negate each other under some circumstances as will be apparent later in describing a comparison between the invention and prior art structures as thus far described.
It is, therefore, a principal object to this invention to provide an improved rotating electrical machine that incorporates permanent magnets and in which the cogging torque is maintained at a low value while vibrations and electrical power output are significantly improved.
It is a further object to this invention to provide an arrangement wherein the power output can be increased and the driving force decreased without adversely affecting the cogging torque.
The vibrational effect may be reduced by decreasing the number of magnets to, for example 6. The cogging number then decreases to 18. Then, however, the cogging torque becomes unacceptably large. Another way in which the vibrational problem may be reduced is by providing a series of magnets which are skewed relative to each other in side-by-side fashion and which cooperate with the coil windings. This type of mechanism is very difficult to manufacture and in fact cannot be manufactured by high production volume techniques.
Therefore, it is a principal object to this invention also to provide an improved and simplified rotating electrical machine that can be manufactured on high speed assembly apparatus and which will have the desired performance.